1. Field of the Invention
The present invention relates to a conveyor apparatus, and in particular, to an adjustable conveyor apparatus for conveying devices, such as printed circuit boards, wherein the length of the conveying apparatus can be adjusted.
2. Discussion of Related Art
The present invention is designed for, but not limited to, use with machines intended to place components on printed circuit boards. For example, Universal Instruments Corporation makes many different types of apparatus for receiving a printed circuit board, and quickly and automatically placing a number of components on the printed circuit board with high precision. See, e.g., U.S. Pat. No. 5,649,356, among others. However, it has been found that one such machine is not always capable of fully populating a particular printed circuit board. In such a case, it is necessary to transfer the printed circuit board from one machine to another machine so that the second machine may continue populating the board with additional components. Such transfer or conveying machines are referred to as edge guide conveyors.
Traditionally, edge guide conveyor modules have been used to convey the printed circuit boards from one machine to another. See, e.g., the 5362I Conveyor or the 5374 Shuttle Transfer Conveyor manufactured and sold by Universal Instruments Corporation of Binghamton, N.Y. The 5362I conveyor includes a pair of parallel belts each of which is designed to support an edge of a printed circuit board to convey the printed circuit board from one populating machine to another. However, the length of the 5362I Conveyor apparatus is fixed. The 5374 Shuttle Transfer Conveyor has a gate that can be opened to allow an operator to pass between adjacent machines.
If the distance between the two populating machines is changed, it is necessary to substitute a conveyor of a different length. As an alternative to substituting a conveyor of a different length, other systems are known that enable blocks to be added on to the end of the transfer rails to increase their lengths, or that include adjustable rails that allow the belt supports in the PC card guide to slide inside one another. In the latter device, a spring or weight is used to load the conveyor belt in order to maintain a uniform tension on the belt.
However, such methods have not been satisfactory. For example, the use of blocks to expand the length of the transfer rails requires additional parts to be kept with the conveyor, and doesn't necessarily provide for precise adjustment of the length of the transfer rails. In other words, the adjusted length is limited to the size of the blocks. With regard to the conveyor devices with adjustable rails, such adjustable rails that slide inside one another have the disadvantage in that they leave an edged exposed on the card guide which potentially catches an edge of the PC board that is being transported on the conveyor. Furthermore, the spring loaded belts limit the load that can be transferred by the conveyor and increase the load on the transfer motor.